Especially for gesture detection there are optical processes in the visible or infrared range. Moreover capacitively acting systems are known that acquire the necessary information by the transmission or disturbance of an electric field. The is circuitry expenditure and the cost connected with the realization of such systems are hitherto high. Another problem in the conventional systems consists in the fact that in applications that require battery operation the electricity requirement of such sensors is crucial for practical applicability. Moreover in some applications component costs and space requirement are important, which in case of mass applications, for example in toy industry, can be determining the field of application.
For a capacitive sensor system the evaluation of the capacitance change of a RC low-pass filter structure is known. As excitation signal a sinusoidal voltage or a square signal is used. As signal indicator for the change, the amplitude or the phase or the time difference compared to a reference signal is evaluated. In both approaches (amplitude or phase) it is the relative change ΔC/C of the capacitance change compared to a basic capacitance C that matters, since by this the sensor sensitivity or the maximum detection range of the sensor is determined. A possibly small basic capacitance is to be aspired therefore for a maximum sensitivity.
The object of the present invention is to provide a capacitively acting sensor system that can be realized with small component expenditure and thus small cost and space requirement and which can be characterized moreover also by a low power consumption, in order to be able to work with batteries with small charging capacitance and/or long service life.
This object is attained solved according to the invention is by a circuit arrangement with the characteristics of claim 1.
With several such systems a two- or three-dimensional position detection is possible. It is also possible to provide several sensor electrodes and to connect them by a multiplexer device successively to the circuit. This multiplexer circuit can be triggered by the microcontroller.
Advantageous embodiments of the circuit arrangement according to the invention are object of the dependent claims.